The invention relates generally to liquid petroleum hydrocarbon blends having improved thermal stability. In particular, the invention relates to the use of nanoscopic additives for chemical modification of aviation jet fuels to achieve high thermal stabilities.
Hydrocarbon liquids, such as distillate fuels (gasoline, diesel fuel, and jet fuel), kerosene, and solvents are known to undergo reactions in the presence of oxygen. These reactions, called autoxidation, increase with temperature and result in the formation of oxidized products (e.g., gums, tars, particulates) causing the fuel to fail under thermal stress.
Many attempts have been made to solve the problem of oxidation of liquid hydrocarbons. The introduction of additives into liquid hydrocarbons has been used successfully for many years. For example, see U.S. Pat. No. 5,382,266, which teaches the application of phosphine and phosphates to distillate fuels to prevent fuel degradation (color degradation, particulate formation, and/or gum formation), and U.S. Pat. No. 5,509,944 which discloses the stabilization of gasoline by adding effective amount of a primary antioxidant, such as phenylene diamine, a hindered monophenol, or mixtures of these, and a secondary antioxidant, such as dimethyl sulfoxide. The combination of phosphine and hindered phenols has been used as a stabilizer in thermoplastic polymers to prevent discoloration. See, U.S. Pats. No. 5,362,783. See also, U.S. Pat. No. 6,475,252 which discloses an additive composition comprising a hindered phenol, a peroxide decomposer, and a phosphine compound to prevent oxidation and peroxide formation.
The U.S. Air Force JP-8+100 program developed an additive package for jet fuel which significantly increases the thermal stability of the fuel, preventing the formation of deposits which result from fuel oxidation within aircraft fuel systems. See Heneghan, S. P., Zabarnick, S., Ballal, D. R., Harrison, W. E., J. Energy Res. Tech. 1996, 118, 170-179; and Zabarnick, S., and Grinstead, R. R., Ind. Eng. Chem. Res. 1994, 33, 2771-2777. The JP-8+100 jet fuel incorporates additives to provide thermal stability to 425° F. At high temperatures (>425°), the JP-8+100 additive package looses effectiveness either due to temperature induced failure of the active mechanisms or due to thermal degradation of the additive compounds themselves.
Thus, while laboratory testing and field implementation of JP-8+100 have been very successful at temperatures up to 425° F., application of similar additive technologies to achieve thermal stabilities on the order of 900° F. is considered unlikely. The difficulty does not lie in the approach—modifying a fuel through the addition of additives remains a cost-effective and efficient method for tailoring a fuel to specific temperature requirements. Rather, the difficulty lies in the fundamental limits imposed by high-temperature chemistry—fuel molecules decompose at high temperatures.
There remains a need for an improved jet fuel additive to inhibit the oxidation of the fuel at high temperatures (>425° F.).